1. Field of the Invention
The present invention is directed generally to systems for monitoring the operating parameters of a steam turbine generator and, more particularly, to systems for monitoring the temperature of the rotating parts within the turbine.
2. Description of the Prior Art
Most turbine blade rows are shrouded to provide some measure of sealing between the stationary and rotating portions of the turbine generator. Shroud segments are arc-shaped structures connected in series to form a circular shroud around the tips of the blades in a blade row. Each shroud segment is typically riveted to three or more blade tips. Thus, a number of shroud segments are needed to completely encircle a row of blades.
Experience has shown that shrouds can fail causing damage to themselves as well as other components of the turbine. One type of failure mode is a rub, common to many or all shroud segments within a row, which causes all the shroud segments in the row to heat up. Excessive heat and centripetal loading causes the shroud segments to yield radially. Such radial movement results in increased contact between the shroud segments and the seal thus generating more heat which results in more radial distortion of all shroud segments in a more or less even manner. One or more shrouds may malfunction as a result of a high temperature induced failure of the attachment mechanisms.
Another problem is caused by windage heating. Windage heating of the turbine blades and shroud segments is caused by friction when the gases in the turbine pass the blades and shroud segments. The turbine is designed such that under normal operating conditions windage heating is not a problem. However, under no load conditions the turbine's rotating components may rotate at excessive speeds thus subjecting the shroud segments (and blades) to excessive windage heating. It is desirable to know the temperatures reached by the shroud segments during such overspeed conditions so that stress, fatigue, and the like can be determined to anticipate future failures of those components.
Despite the desirability of monitoring the temperatures of the shroud segments, the harsh environment inside the turbine, extreme speeds at which the rotating portion of the steam turbine travels, and telemetry problems inherent in the use of temperature sensors carried by the rotating portion of the turbine have presented obstacles to the monitoring of those temperatures. Thus, the need exists for a system for monitoring the temperature of the turbine blade shrouds.